This invention relates to improved methods and apparatus for display and biofeedback training of respiratory performance in the use of aerosol drug particles and/or mists from Metered Dose Inhaler (MDI) devices. Hillsman is incorporated herein by reference U.S. Pat. No. 3,991,304.
Medical research indicates aerosol administered medications for bronchial therapy in such conditions as asthma, chronic bronchitis and emphysema is generally the preferred dosage technique for reasons of efficacy, reduced side effects and economy. Such particulate drugs are commonly prescribed using MDI type devices. However, in order to achieve these desirable benefits the medication must be inhaled properly for drug delivery to the required site of therapeutic need, namely, the bronchial tubes deep within the lungs. It is well recognized that improper inhalation technique in the use of MDI devices is a serious barrier to effective therapy. Young and elderly patients in particular are subject to improper MDI use, as such patients frequently have problems with learning and coordination of the required technique, as discussed in "Inhalation Aids of Metered Dose Inhalers" (Chang Shim, M.D., CHEST: Vol.9l #3, p315, Mar. 1987).
Patients commonly have difficulty in the use of conventional MDI devices especially in terms of controlling inhalation, and proper activation timing of the MDI delivery system. Typically, among other less common errors, patients will inhale too fast, or in an erratic manner. Frequently they will delay activation of the MDI device until after inspiration has started, and therefore, the crucial initial portion of the inspired breath does not contain medication.
Frequently patients will begin the MDI inspiration breath at an improper level of lung volume, for example, their lungs may already be relatively full of air and therefore a proper large volume of inspired air is impossible. The precise level of desirable initial lung volume is a matter of scientific debate, but most authorities agree it is somewhat less than the so-called Resting Expiratory Level, i.e. the lung volume at the end of normal expiration.
Frequently patients will not inhale the MDI breath to the adequate extent of lung capacity. The desired inspiration volume is also a matter of debate, but most authorities agree it is somewhere just below the so-called Total Lung Capacity, i.e. the maximum possible inspiration lung volume.
Once the proper MDI inspiration breath has been achieved, it is important for the patient to sustain a brief period of breath holding. During this time the medicated mist accumulates moisture, and the aerosol particles become larger and heavier, and therefore are de-entrained or "rain out" from the aerosol suspended state and deposit in the airways. The desired time interval of breath holding is generally thought to be about five to ten seconds. However, this desirable time may be functionally limited, as dictated by individual patient needs and breath holding capabilities.
While it is generally felt the timing of MDI activation should be simultaneous with the beginning of inspiration, there is a minority scientific opinion that questions whether said activation should be a fraction of a second before or after the beginning of inspiration. However, it is understood that these events are substantially concurrent.
It should be apparent from the above, that while the act of using an MDI device may appear simple, it is in fact a complex act, and the proper performance of this technique is crucial to the optimal delivery of drugs to the bronchial airways. Without proper MDI inhalation technique, the patient may in fact derive little or no benefit from this form of drug therapy.